The present invention relates to a mold for manufacturing plastic items, particularly screw caps.
Various processes and machines for pressure-molding plastic items are known; one of these machines is known for example from WO 96/09153 in the name of this same Applicant and comprises a carousel which can rotate about a vertical axis and on which a plurality of angularly spaced molding units are mounted. Each unit comprises an upper male mold half which is aligned with a lower female mold half. A dose of semi-fluid plastic material is fed into the molding cavity of said female mold half and is pressed by means of a relative movement of the two mold halves.
When the items to be manufactured have a limited height in the molding direction and therefore the cavity of the female mold half has a shallow containment wall, problems can arise in retaining the dose of plastics within the cavity. The dose deposited in the molding cavity, being subjected to centrifugal force, in fact tends to escape radially and to remain trapped between the male mold half and the female mold half, forming flash.
The aim of the present invention is to obviate the above-noted drawbacks of conventional devices, i.e., to provide a mold for manufacturing plastic items, particularly caps, which allows to retain within the cavity of the female mold half the dose of semi-fluid plastic material independently of the final shape of the manufactured item without this detracting from the precision of the centering between the male mold half and the female mold half.
Within the scope of this aim, an object of the present invention is to provide a mold which is simple, relatively easy to provide in practice and applicable to conventional devices without having to resort to substantial modifications thereof.
This aim is achieved by the present mold for manufacturing plastic items, composed of a female mold half and of a male mold half which are mutually aligned along a vertical axis, said male mold half being composed of a sleeve and a plug which is guided inside said sleeve and is movable with respect thereto, characterized in that said female mold half comprises a base plate, a bush which is guided on said base plate and forms, together with said base plate, a cavity for receiving a dose of plastic material to be molded, said bush being provided with an abutment which acts as a locator for said sleeve during molding, said bush being movable with respect to said base plate in contrast with elastic return means which allow said plug to enter said cavity.